(Na1-xKx)0.5Bi0.5TiO3 (NBT-KBT-100 x) thin films were deposited on Pt/Ti/SiO2/Si(100) by metal organic decomposition, and the effects of potassium content (x = 0.15, 0.18, 0.20, 0.25) on ferroelectric, piezoelectric, dielectric properties of the thin films, and the temperature dependence of dielectric permittivity of NBT-KBT-18 thin film were investigated in detail. NBT-KBT-18 thin film is of the largest effective piezoelectric coefficient d33eff, remnant polarization 2Pr, spontaneous polarization 2 Ps, dielectric constant ɛr, and the lowest dielectric loss among the thin films. The dielectric constants decrease steeply with the increase of frequency, and there are a series of resonance peaks with Debye-like relaxation. In dielectric temperature spectra, two abnormal peaks corresponding to depolarization temperature and Curie temperature are at the range of 75-90 °C and 295-320 °C, and they are associated with the phase transitions. Based on the dielectric relaxation theory, Debye-like relaxation and diffused phase transition/frequency dispersion are interpreted by space charge polarization and polar nanoregions. Because of the centrosymmetric paraelectric phase, the 2 Ps and ɛr of NBT-KBT-100 x thin film are responsible for the d33eff according to phenomenological equation. The improved d33eff may make NBT-KBT-18 thin film a promising candidate for piezoelectric thin film devices, and the enhanced Curie temperature will offer useful guidelines of safe working temperature for potential application in micro-electro-mechanical system.
Modeling of the hysteresis loop of ferroelectric thin films has been thought very difficult owing to its nonlinear and history-dependent electric field effects. Here we extend the Preisach model [Z. Phys. 94, 277 (1935)] by using the distribution function integral and superposition method. The model shows improved hysteresis loop that agrees reasonably well with the experimental data measured from the bismuth layer-structured ferroelectric thin films. Compared with the previous model, the current model provides polarization-field (P-E) loop with full and symmetric shape, suitable coercive field (Ec), and few undesirable parameters. The butterfly loop of perovskite-type ferroelectric thin films is also simulated. Additionally, the approach is able to describe the unsaturated loops obtained under various ac electric fields, which is very useful in circuit simulation of ferroelectric field effect transistor or ferroelectric capacitor.
Abstract Because of their good performance in diffusion‐limited processes, ordered macro‐microporous single‐crystalline metal‐organic frameworks (MOFs) have potential for use in various fields. However, there are still very few reports of the synthesis of such MOFs. A general synthesis methodology for ordered macro‐microporous single‐crystalline MOFs is highly desired. Here, a novel strategy is reported for synthesizing single‐crystalline ordered macro‐microporous MOFs by monodentate‐ligand‐induced in situ crystallization within a 3D ordered hard template in a double‐solvent system. A space‐confined growth model is proposed to clarify the shaping effect of the template; the role of the monodentate ligand is also analyzed. Moreover, a carbon material derived from the macro‐microporous MOF inherits the ordered interconnected macroporous structure. The improved diffusion and lower resistance, as well as the structural robustness, endow the derivative carbon material with superior rate performance and excellent cycling stability when prepared as electrodes for a supercapacitor. It is anticipated that the method will provide new paths to the synthesis of such macro‐microporous materials for applications in energy‐related fields and beyond.
This paper introduced a strategy for parallel implementation of the FDTD algorithm used in COW(Cluster of Workstation)parallel computing system and PVM parallel environment.Because of the one dimension space division,this method is efficient relatively highly efficient.Some computed examples were given to prove the feasibility and correctness of this method.This method provides a solve scheme for the EM computation of electrically large size complex object and can be used in radiation,scattering and EMC analysis.
In this letter, we introduce an improved model, which is based on the Miller model, with a thin nonswitching interface layer near the top electrode to describe the channel current of the metal-ferroelectric-insulator field-effect transistor (MFIS-FET). In our model, the thickness ratio O of the nonswitching interface layer varies for different failure mechanisms or external applied electric voltage. Theoretical prediction based on this approach agree well with the recent experiments showed by Tabuchi et al. [Integrated Ferroelectrics 79, 211 (2006)].
N, O-Carboxymethyl chitosan (N, O-CMC) was synthesized in this study, and the properties of N, O-CMC were affected by the synthesis conditions. Structure of N, O-CMC was detected by fourier transform infrared spectrum (FTIR) and X-ray powder diffraction (XRD) was used to analyze the crystallinity. Potentiometric titration was used to measure the DS of N, O-CMC.
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